The long range goal of the proposed research project is to obtain an understanding of the mechanisms of regulation in eukaryotic cells and to relate such information to the metabolism of cancer cells. The yeast Saccharomyces will be used as a model system. In yeast, the biogenesis of mitochondria and the synthesis of the maltose, galactose and sucrose fermentation enzymes is repressed by glucose. Methods are described by which one may isolate mutants of the catabolite repression system. One method involves the use of glucosamine known to act as a gratuitous catabolite repressor in Saccharomyces inhibiting growth on lactate, maltose, and galactose. Mutants capable of growth on any of these carbon sources in the presence of glucosamine will be isolated. It is expected that a high proportion of these mutants will be insensitive to glucose in their ability to 1. elaborate a functional mitochondrion and/or to 2. synthesize the maltose, galactose and sucrose fermentative enzymes. The four classes of mutants to be isolated will be compared as to which glucose sensitive functions have been affected when the different selective procedures are used.